getdayname.js

  // Returns 'yesterday', 'today', 'tomorrow', or else the full day name 
  getDayName(mo) {
    const daysDifferenceToToday = mo.startOf('day').diff(moment().startOf('day'), 'days');

    const differenceMask = {
      '-1': 'Yesterday',
      0: 'Today',
      1: 'Tomorrow'
    };

    return differenceMask[daysDifferenceToToday] || mo.format('dddd');
  }